1. Field of the Invention
The present invention relates to a structure of a power train system comprising an engine, a rotary electric unit and a gearbox and more particularly to a power transmission system for increasing a power transmission efficiency in the power train system. (In this specification, we define the rotary electric unit as an electric motor when it is mainly used to drive, a generator when it is used to generate electric power and start the engine, or a motor generator when it is used to generate electric power as often as to drive.)
2. Related Background Art
From the viewpoint of global ecology, the world has been carefully watching the development of a hybrid car control system which is assumed to drastically reduce the fuel ratio.
Japanese Non-examined Patent Publication No. 10-217779 (1998) has disclosed a unified hybrid power transmission system comprising one rotary electric unit, a reduction gear mechanism, and a clutch mechanism.
In this publication, a power transmission system houses a rotary electric unit and a clutch mechanism in its casing to make the power train system compact and light-weighted.
By always joining together the input shaft of said gearbox and said rotary electric unit, the power transmission system can cause the engine to drive only said rotary electric unit to generate electric power and use part of the generated power to cause the other rotary electric unit to run. This is what is called a series hybrid driving mechanism.
This hybrid power transmission system totally controls the engine and the rotary electric unit so as to give a satisfactory acceleration/deceleration feeling to the driver and run the engine and the rotary electric unit at a high efficiency.
Said unified hybrid power transmission system disclosed in Japanese Non-examined Patent Publication No. 10-217779 (1998) has problems as stated below.
The first problem is that the rotary electric unit must be provided closer to the driving shaft (rather than to the reduction gear mechanism) to reduce torque shocks caused by changes of reduction gears (e.g. from First to Second gear positions and Second to Third gear positions). However, to generate electric power by the driving force of the engine in the series hybrid mode, the rotary electric unit must be provided closer to the engine (rather than to the rotary electric unit). Therefore, to increase the speed change performance while reducing reduce torque shocks caused by gear changes, said system must be equipped with at least two rotary electric units, which makes the system greater.
The second problem is that the mechanism for transmitting the drive (torque) from the output shaft of the engine to the output shaft of the rotary electric unit is very complicated and consequently it has a low torque transmission efficiency.
The third problem is that the inertia torque of the revolving shaft of the rotary electric unit works on the engine as a load as said unified hybrid power transmission system houses the engine and the rotary electric unit in a body. Therefore, when the system tries to accomplish an acceleration command made by the driver, the engine must generate a torque required for the acceleration command and a torque enough to cancel said inertia torque. Consequently, the fuel ratio goes lower when the drivability is increased.
Judging from the above problems, an object of the present invention is to provide a power transmission system comprising a reduction gear mechanism housing, a rotary electric unit and clutch mechanism which cab be increase the efficiency of the power transmission, reduce the fuel ratio of the car, and make the driving system more compact.
The aforesaid problems can be accomplished by improving the reduction gear mechanism by the invention disclosed below.
The first one of said problems can be effectively solved by providing a mechanism which mechanically absorbs the gear change shock instead of using an electric driving force such as a rotary electric unit. In other words, the present invention is a power transmission system for an automobile comprising an engine, a gearbox placed between said engine and a driving shaft, a rotary electric unit connected to the output shaft of said engine and to said driving shaft through said gearbox, and a clutch placed between the input shaft of said transmission unit and the output shaft to control the transmission torque from the output shaft to the input shaft. This clutch can absorb gear change shocks without any rotary electric unit near the driving shaft.
Preferentially, said clutch is a power gearbox of a car which is mounted on a gear of the minimum gear ratio (on a HIGH gear) in said reduction gear. In other words, the clutch mounted on the HIGH gear side can handle any rotational change before and after gear changes.
Further, the second one of said problems can be effectively solved by a technique disclosed below. Usually, a hybrid car stops the engine when the car stops and restarts the engine by the rotary electric unit when the car starts to run to increase the fuel ratio of the engine. In this case, it is more effective to reduce the revolution of the gearbox by the gearbox and transmit it to the engine shaft instead of directly transmitting the revolution of the gearbox to the engine shaft. In other words, the system in accordance with the present invention is a power transmission system of an automobile comprising an engine, a gearbox placed between said engine and a driving shaft, and a rotary electric unit connected to the output shaft of said engine and to said driving shaft through said gearbox, wherein the drive (rotation) of the output shaft of said rotary electric unit is reduced and transmitted to the input shaft of said gearbox in the side facing to the engine.
Further, it is effective to reduce the number of transmission mechanisms such as gears which transmit the drive of the engine to the rotary electric unit when driving the rotary electric unit by the drive of the engine to generate electric power. In other words, the system in accordance with the present invention is a power transmission system of an automobile comprising an engine, a gearbox placed between said engine and a driving shaft, and a rotary electric unit connected to the output shaft of said engine and to said driving shaft through said gearbox. The efficiency of power transmission can be retained by directly engaging the gear of the output shaft of the engine and the gear of the output shaft of the rotary electric unit (without any gear between said gears).
Further the system is preferentially equipped with a clutch which disconnects the output shaft of said rotary electric unit from the input shaft of said gearbox (closer to said rotary electric unit. As this clutch disconnects the engine from the rotary electric unit and prevents the inertia torque of the rotary electric unit from giving a load to the engine. Thus the third one of said problems can be solved.
According to the present invention, a clutch mechanism provided to join together and disconnect the input shaft and the output shaft of the gearbox can absorb gear-change shocks which generate in speed changes without adding a rotary electric unit closer to the axle that to the gearbox.
Further, the electric efficiency of restarting the engine can be increased by building up the system so that the drive of the output shaft of the rotary electric unit may be reduced and transmitted to the input shaft of the engine.
Furthermore, reduction in efficiency of power generation by the engine can be suppressed by direct engagement of gears of the output shaft of the engine and the output shaft of the rotary electric unit.
When equipped with a clutch which disconnects the output shaft of the rotary electric unit and the input shaft of the gearbox (in the side of the rotary electric unit), the power transmission system can disconnect the engine and the rotary electric unit to prevent the inertia torque of the rotary electric unit from acting as a load on the engine.